1. Field of the Invention
The present invention pertains to fiber optic communications systems and, more particularly, to monitoring devices and methods for monitoring shifts in optical crossconnect configurations utilizing micro electromechanical systems (MEMS) tilting mirror arrays.
2. Description of the Related Art
In fiber optic communication systems, signal routing is essential for directing an optical signal carrying data to an intended location. Existing routing techniques typically experience optical power loss due to inefficient coupling of optic signals between input and output fibers. This increases the dependence on optical power sources (e.g., pump lasers) which are used to compensate for power losses by injecting optical power back into the optical system. The need for optical power sources increases the overall cost of the optical system.
Another criteria for signal routing is the ability to direct a signal received from one of a plurality of input fibers or ports to any of a plurality of output fibers or ports without regard to the frequency of the optical signal.
Free-space optical crossconnects allow interconnecting among input and output ports in a reconfigurable switch fabric. An example of such an optical crossconnect utilizing mirco-electromechanical systems (MEMS) tilting mirror devices is disclosed in commonly owned and copending U.S. patent application Ser. No. 09/410,586, filed Oct. 1, 1999. By adjusting the tilt angles of the MEMS mirror devices, optical signals can be directed to various destinations, i.e. to numerous output fibers.
MEMS devices and, in particular, tilting mirror devices are susceptible to unwanted movement or drift due to external factors such as temperature changes and mechanical fatigue experienced by actuator elements used to deploy and control the individual mirror elements. As a result, optical signal power may be lost due to misalignment of the reflected optical signal with its intended target (e.g. an output fiber). Accordingly, a system is desired to monitor MEMS optical crossconnect configuration to provide for displacement adjustment.
An optical crossconnect device having a monitoring feature for detecting optical signal drift is provided. The device provides optical connection of optic signals between input fibers and output fibers by using a MEMS tilt mirror array. The MEMS array includes a plurality of tiltable mirror elements which are positionable in an intended orientation for directing optical signals, but which are susceptible to drift that causes degradation in the optical coupling of the signals to the output fibers. A monitoring device positioned outside of the optical path dynamically monitors the position of one or more of the mirror elements to detect drift.
In a preferred embodiment, the monitoring device is a camera for obtaining an image of one or more mirror elements.
In another embodiment, the monitoring device comprises an optical transmitter and an optical receiver for transmitting a test signal through the optical crossconnect to monitor mirror position drift.
In yet another embodiment, a pattern is formed on one or more of the mirror elements and an image or reflection of the pattern is obtained for determining the presence of mirror drift.
A method is also described for monitoring mirror element positions of mirror elements in a MEMS tilt mirror array used in an optical crossconnect. The method is used with a MEMS mirror array having mirror elements disposed at desired tilt positions for crossconnecting an optic signal between an input fiber and an output fiber along an optical path. A monitoring device disposed outside of the optical path monitors the positions of the mirror elements to detect when position drift occurs. The mirror positions are then adjusted by forming control signals based on the detected drift and applying the control signals to the drifted mirror elements.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate and explain the structures and procedures described herein.